The present invention relates to field effect transistors (FETs), and more specifically, to reducing negative bias temperature instability (NBTI).
NBTI deterioration occurs over a period of use and results in an increase in threshold voltage over that period. NBTI affects the reliability of field-effect transistors (FETs) and, because they operate with negative gate-to-source voltage, p-channel FETs (pFETs) in particular. NBTI is known to be related to nitrogen incorporation into the silicon/silicon dioxide (Si/SiO2) interface and results in an increase in threshold voltage. Nitride metal (e.g., titanium nitride TiN), which is commonly used as a pFET work function setting metal, may cause such nitrogen incorporation and result in deteriorated NBTI.